1. Field of the Invention
This invention relates to 4,4'-methylene-bis-(2-ethyl-5-methyl imidazole), used effectively as a curing agent or a cure accelerating agent of an epoxy compound or a crystallization retarder of 2-ethyl-4-methyl imidazole and to methods of producing and using the same.
2. Prior Art
Since epoxy resins are generally excellent in electrical insulation, mechanical strength, and resistance to chemicals, they are widely used in various industrial fields, and as curing agents, various curing agents are used such as fatty polyamine, aromatic polyamine, amine salt, tetraammonium salt, dicyanodiamide, urea, melamine, polycarboxylic acid, polycarboxylic acid anhydride, polyvalent phenol containing added condensate of phenols and aldehydes, polycarboxylic acid hydrazide, 2-ethyl-4-methyl imidazole.
Of the curing agents mentioned above, 2-ethyl-4-methyl imidazole (hereinafter referred to as "2E4MZ") is by nature a normal temperature crystallizable substance having a melting point of about 45.degree. C. but 2E4MZ obtained immediately after having been refined by distillation under reduced pressure provides a liquid state for a considerably long time at normal temperature due to a supercooling phenomenon. Such liquid 2E4MZ is excellent in its compatibility with epoxy resin, it is highly valued as a curing agent or cure accelerator for the epoxy resin and is used today on a worldwide basis.
But this liquid 2E4MZ develops crystalline nuclei when the supercooling phenomenon is broken and rapidly solidifies in its entirety by the growth of crystals. When 2E4MZ solidifies in this manner, it is reduced in compatibility with epoxy resin, so that users tend to shun 2E4MZ liable to crystallize. The difficulty or ease with which 2E4MZ crystallizes depends upon the purity of 2E4MZ. Generally the higher in purity it is, the more easily it crystallizes and the lower in purity, the less liable it is to crystallize. However, it is difficult to find an ideal product high in purity and yet without atendency to crystallize from products of 2E4MZ commercially obtainable.
The present inventors have become confident during their course of research on 2E4MZ that compounds related to 2E4MZ must also be effective for use as curing agents or accelerators for epoxy resin, and have set about developing a new compound related to 2E4MZ.
Various compounds are thought to be related with 2E4MZ, and on the presumption that compounds most akin in property to 2E4MZ will be bis-compounds having 2E4MZ of two molecules bonded with an alkylene group, the inventors have attempted to synthesize the bis-compounds. But it is not an easy task to synthesize the compounds and after repeated failures, we have finally succeeded in synthesizing desired bis-compounds with good yield by heating 2E4MZ and formaldehyde or a methylenizing agent in the presence of a catalyst. The inventors have found that the 4,4'-methylene-bis-(2-ethyl-5-methyl imidazole) synthesized in this manner is effective for use as a curing agent or a cure accelerator for epoxy resin and, in addition, it is highly effective also for use as a crystallization inhibiting agent and have worked out the present invention.